1. Field of the Invention (Technical Field)
The present invention relates to thermography. More particularly, the present invention relates to a method and apparatus for displaying more than one infrared image to permit visual comparison of objects within the field of view of the apparatus.
2. Description of Related Art
Note that the following discussion refers to a number of publications by authors and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Motor vehicle brake components play an essential role in contributing to safety on our nations highways. As such, several inventions have been developed to detect cold brake components which indicate that the brake is not functioning properly. The majority of theses inventions measure the gross thermal radiation emitted by everything contained within their field of view. For example, a prior art device focused at a wheel and brake assembly would be incapable of determining if the tire or the brake was overheating. This is because many prior art devices return only one gross radiation value for the entire area in the field of view. Since these devices are incapable of determining precisely what component is emitting the greatest amount of thermal radiation in their field of view, it is often desirable for them to have the smallest field of view possible, thus enabling the user to determine only the radiation of the component contained within the field of view of the device.
U.S. Pat. No. 5,942,753, to Dell, entitled “Infrared Remote Sensing Device and System for Checking Vehicle Brake Condition”, discloses a device for determining the thermal condition of vehicle brakes. An infrared sensing device having two detectors measures infrared radiation being emitted by each brake. The measurements obtained are then sent to a computer which then displays two values representative of the measured radiation of the two brakes together with a video image of the truck taken by a conventional video camera.
U.S. Pat. No. 5,478,151, to Duhrkoop, entitled “Device for Detecting Excessively Heated Components or Locations in Moving Objects”, discloses the use of an infrared beam detector and separate lenses, each aimed at a separate measuring point, as well as a movable mirror for alternately focusing the infrared beam on a single radiation detector.
U.S. Pat. No. 5,007,432, to Keller et al., entitled “Radiation Detection Method and Apparatus”, discloses focusing beams of radiation from spatially separate areas of a human body onto a single radiation detector. The radiation detector preferably used is an infrared detector which produces an electrical output when a thermal differential is detected.
U.S. Pat. No. 4,682,029, to Diepeveen et al., entitled “Stereoscopic Infrared Imager Having a Time-Shared Detector Array”, discloses a device which uses two mirrors, each capturing an infrared image, and two rotating mirrors that scan the fields of view provided by the two static mirrors and directs the radiation to a single radiation detector, the measured alternating temperature values then being displayed on separate display devices.
None of the devices of the aforementioned patents are capable of determining a radiation imbalance nor are they capable of creating and displaying a thermal image on a visual display apparatus. There is thus a present need for a method and apparatus which will enable more than one infrared image to be displayed on a viewing apparatus, thus enabling a user to quickly and easily perceive differences between the two thermal images and thereby not only determine which component has an unusual, unexpected or abnormal thermal signature, but also determine which specific area (and therefore which component) of the field of view has an irregular temperature.